ssh-keyscan (1)
Leading comments
$OpenBSD: ssh-keyscan.1,v 1.38 2015/11/08 23:24:03 jmc Exp $ Copyright 1995, 1996 by David Mazieres <dm@lcs.mit.edu>. Modification and redistribution in source and binary forms is permitted provided that due credit is given to the author and the OpenBSD project by leaving this copyright notice intact.
NAME
ssh-keyscan - gather ssh public keysSYNOPSIS
ssh-keyscan -words [-46cHv [-f file ] ] [-p port ] [-T timeout ] [-t type ] [host | addrlist namelist ] ...
DESCRIPTION
ssh is a utility for gathering the public ssh host keys of a number of hosts. It was designed to aid in building and verifying ssh_known_hosts files. ssh provides a minimal interface suitable for use by shell and perl scripts.ssh uses non-blocking socket I/O to contact as many hosts as possible in parallel, so it is very efficient. The keys from a domain of 1,000 hosts can be collected in tens of seconds, even when some of those hosts are down or do not run ssh. For scanning, one does not need login access to the machines that are being scanned, nor does the scanning process involve any encryption.
The options are as follows:
- -4
- Forces ssh to use IPv4 addresses only.
- -6
- Forces ssh to use IPv6 addresses only.
- -c
- Request certificates from target hosts instead of plain keys.
- -f file
- Read hosts or ``addrlist namelist'' pairs from file one per line. If - is supplied instead of a filename, ssh will read hosts or ``addrlist namelist'' pairs from the standard input.
- -H
- Hash all hostnames and addresses in the output. Hashed names may be used normally by ssh and sshd but they do not reveal identifying information should the file's contents be disclosed.
- -p port
- Port to connect to on the remote host.
- -T timeout
- Set the timeout for connection attempts. If timeout seconds have elapsed since a connection was initiated to a host or since the last time anything was read from that host, then the connection is closed and the host in question considered unavailable. Default is 5 seconds.
- -t type
- Specifies the type of the key to fetch from the scanned hosts. The possible values are ``rsa1'' for protocol version 1 and ``dsa'' ``ecdsa'' ``ed25519'' or ``rsa'' for protocol version 2. Multiple values may be specified by separating them with commas. The default is to fetch ``rsa'' ``ecdsa'' and ``ed25519'' keys.
- -v
- Verbose mode. Causes ssh to print debugging messages about its progress.
SECURITY
If an ssh_known_hosts file is constructed using ssh without verifying the keys, users will be vulnerable to man in the middle attacks. On the other hand, if the security model allows such a risk, ssh can help in the detection of tampered keyfiles or man in the middle attacks which have begun after the ssh_known_hosts file was created.FILES
Input format:1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
Output format for RSA1 keys:
host-or-namelist bits exponent modulus
Output format for RSA, DSA, ECDSA, and Ed25519 keys:
host-or-namelist keytype base64-encoded-key
Where keytype is either ``ecdsa-sha2-nistp256'' ``ecdsa-sha2-nistp384'' ``ecdsa-sha2-nistp521'' ``ssh-ed25519'' ``ssh-dss'' or ``ssh-rsa''
/etc/ssh/ssh_known_hosts
EXAMPLES
Print the rsa host key for machine hostname$ ssh-keyscan hostname
Find all hosts from the file ssh_hosts which have new or different keys from those in the sorted file ssh_known_hosts
$ ssh-keyscan -t rsa,dsa,ecdsa,ed25519 -f ssh_hosts | \
sort -u - ssh_known_hosts | diff ssh_known_hosts -